Media captionMr Obama said the US could not turn a blind eye to what had happened in Damascus

President Barack Obama says the US should take military action against Syria and he will seek congressional authorisation for intervention.

The US says the Syrian government carried out chemical weapons attacks on 21 August in which 1,429 people died.

Mr Obama said the operation would be limited in duration and strong to deter future chemical attacks. Congress is due to reconvene on 9 September.

The Syrian government denies it was behind the attacks and blames rebels.

UN inspectors who have been investigating the attacks arrived in the Netherlands on Saturday with samples from site visits, which will be tested in laboratories in Europe.

The Organisation for the Prohibition of Chemical Weapons, which is overseeing the investigation, said the whole testing process could take up to three weeks, although "every effort" would be made to expedite it.

Senior White House officials told the BBC's Katty Kay that Mr Obama's decision to seek congressional approval was made by the president on Friday afternoon. It had not been planned until then.

The officials added that they believed they would get congressional approval, although they were aware of the risks, our correspondent adds.

Later on Saturday, Mr Obama formally asked Congress to authorise military action.

The draft legislation seeks approval for the use of force to prevent the Syrian government from carrying out chemical weapons attacks.

'No blind eye'

Analysis

President Obama was elected to end America's wars, and in reaction to the fallout of the invasion of Iraq. He knows, as he frankly admitted, that Americans are "weary of war". Many of his own supporters want him to focus on what he calls "nation-building at home".

But he is trapped within his own red lines and perhaps the need to send a signal to Iran and North Korea. White House sources say the British vote shows the dangers of allowing a debate - but it also removed a key ally and so, ironically, made support at home even more vital.

It also increased the demands from Congress itself to have a say. A recent poll indicated 80% of Americans thought Congress should vote before any military action. Some will say the decision shows President Obama is weak. It certainly shows the weakness of his position - he wants to take action that isn't popular and home or abroad.

But it is sensible to make sure the responsibility for unpopular action is shared with other politicians, and canny for domestic reasons to keep a very sour Congress sweet. Some might even argue that, in a democracy, it is the right thing to do.

President Obama said the US was prepared to strike whenever it chose. "Our capacity to execute this mission is not time-sensitive."

He added: "We cannot and will not turn a blind eye to what happened in Damascus."

Mr Obama says he has the constitutional authority as commander-in-chief to order military action without the backing of Congress.

However, he said it was important to have the debate.

Senate Republican Leader Mitch McConnell welcomed the announcement, saying the president's role as commander-in-chief was "always strengthened when he enjoys the expressed support of the Congress".

Republican Senators John McCain and Lindsey Graham, who have been pushing for US intervention in Syria, also gave their backing to the vote.

However, they warned against limited strikes which would not change the balance of the conflict, calling the prospect "an inadequate response to the crimes against humanity that [Syrian President] Assad and his forces are committing".

The BBC's Katy Watson in Washington says that if Mr Obama is to intervene, he wants the people - and politicians - on his side.

100 videos attributed to the attack show symptoms consistent with exposure to a nerve agent

Communications were intercepted involving a senior Damascus official who "confirmed chemical weapons were used" and was concerned about UN inspectors obtaining evidence

Syrian President Bashar al-Assad has said his country will defend itself against any Western "aggression".

Forces which could be used against Syria:

•Four US destroyers - USS Gravely, USS Ramage, USS Barry and USS Mahan - are in the eastern Mediterranean, equipped with cruise missiles. The missiles can also be fired from submarines, but the US Navy does not reveal their locations

•Airbases at Incirlik and Izmir in Turkey, and in Jordan, could be used to carry out strikes

•French aircraft carrier Charles de Gaulle is currently in Toulon in the western Mediterranean

•French Rafale and Mirage aircraft can also operate from Al-Dhahra airbase in the UAE

Correction 3 September: An earlier version of the story stated that President Obama has the constitutional authority to order military action without the backing of Congress. The story has been amended to make it clear that this is the view of the Obama administration.